It does, but seeing as there is most likely a very small intersection between the code for ROS 1 and ROS 2, what would be the benefit apart from reducing the nr of repositories? Chances for cherry-picking are most likely slim (not zero though).
One reason would be to not tie versioning (ie: releases and history) to that of the ROS wrappers.
As nice as ROS is, there are other frameworks/middlewares/software systems out there, and separating things out like this makes integration with those easier (perhaps not just technically, but also psychologically: I’ve seen companies refuse to use particular pieces of software just because it was hosted “somewhere” that they associated with bad practices and NIH).